Low power consumption and reliable selectivity are the two main requirements for gas sensors to be applicable in mobile devices. [1] These technological platforms, e.g. smart phones or wireless sensor platforms will facilitate personalized detection of environmental and health conditions, and hence becoming the basis of the future core technology of ubiquitous sensing. Even today, health control as well as environmental monitoring is relying on immobile and complex detection systems with very limited availability in space and time. Recent works have shown promising concepts to realize selfpowered gas sensors that are capable of detecting gases without the need of external power sources to Submitted to 2 activate the sensor-gas interaction or to actively generate a read out signal. [2,3] These sensors drastically reduce power consumption compared to conventional semiconductor gas sensors and additionally reduce the required space for integration. All these attempts so far were based on purely nano structured inorganic metal oxide sensor materials that provide a good sensitivity towards different gases due to their high surface-to-volume ratio. However, due to their non-selective sensing mechanism based on oxygen vacancy-gas interactions, these purely inorganic sensors cannot accomplish a meaningful gas selectivity. [4,5] High selectivities towards single gas species have been recently reported via modifying the inorganic surface of nanostructured semiconductors with a defined organic functionality. [6][7][8][9] Theoretical simulations based on ab-initio density functional theory (DFT) for a system composed of SnO2 NWs modified with a defined self assembled monolayer (SAM) elucidated the reason for the high selectivity of such gas sensor: the energetic position of the SAM-gas frontier orbitals with respect to the NW Fermi level have been identified to be the crucial factor to ensure an efficient charge transfer upon gas-SAM binding interactions and thus to sense or discriminate a certain gas species. [7] The high flexibility of organic surface modifications in terms of functional groups as well as their sterical and electronic structure possibly might enable the targeted design of various specific gas sensors. However, all organic surface modified sensor systems so far are based on compact conductometric or field effect transistor (FET) sensor concepts that still require a remarkable amount of energy to generate a sensor signal (e.g. by applying a source-drain current). Up to date, none of the semiconductor based gas sensor systems could accomplish both, the selfpowered/low powered sensor operation and highly selective gas detection within a single and compact device.In this work, we present a semiconductor based gas sensor concept that combines the two substantial requirements of mobile gas sensing in a singular sensor device: self-powered operation combined with high gas selectivity. Beyond the combination of self-powered sensing and high selectivity, also a very high sensitivity could also been demonst...

Vacuum hydrogen annealing of TiO2 leads to increased visible light absorption. The origin thereof was revealed by ab initio calculations and X-ray photoelectron spectroscopy.

The efficient separation of photogenerated electron-hole pairs and stability against corrosion are critical preconditions for a photoelectrode to achieve a high photoelectrochemical performance. In this work it is shown how both criteria can be met by employing a heterostructure of bismuth vanadate (BiVO4) and titanium dioxide (TiO2) as the photocatalyst. Using electronic structure calculations, an alteration of the band alignment is predicted at the heterojunction from type I to type II by hydrogen treatment of the top TiO2 layer. Guided by this idea, we have fabricated heterostructures of BiVO4 and TiO2 and studied the effect of hydrogen treatment. The achieved band engineering results in a significant improvement in photocurrent density, up to 4.44 mA cm-2 at 1.23 V vs RHE, and a low onset potential, -0.14 V vs RHE, under visible light illumination